Heading into the final stretch of a year-long trial run, the experimental net-zero energy house at the National Institute of Standards and Technology (NIST) in Gaithersburg, Md., must overcome an energy deficit of 154 kilowatt hours—equivalent to about $20—during the month of June.

The facility was designed to produce at least as much energy as it consumes over the course of a year. At the end of May, the research residence still owed on its total energy bill, which averaged less than $2.00 a month over the first 11 months. In contrast, the monthly expenditure for electric power alone averaged $129 for Maryland households in 2012, according to the U.S. Department of Energy.